It's a valve that's over your head

Mainly, the difference is that in an overhead cam engine, the camshaft is mounted on the head of the engine, and the valves are still overhead, in an overhead valve engine (sometimes called a "pushrod motor"), the camshaft is in the crankcase.

Under the valve cover, of an overhead valve engine.

They push the rockers on the opposite side of the valve stems.

Overhead Cam engines do not have push rods.

Fewer moving valve train parts such as the push rods.

Single Overhead Valve Engine